Conventional reciprocating engine (or internal combustion) generator sets are commonly used for standby and emergency power. In the event of a power outage in a building or facility, these reciprocating engine generator sets can be started to provide power for the building or facility. The high maintenance requirements make reciprocating engine generator sets unsuitable, however, for continuous load applications, such as base loading, peak shaving, and load following. In addition, reciprocating engine generator sets cannot be used for sustained load applications in non-attainment zones since their high emission levels do not meet current regulatory requirements for continuous operation. The expense of downtime, however, can easily justify a relatively low cost reciprocating engine generator set for standby.
On the other hand, a turbogenerator has low emission levels and grid parallel operational features ideal for continuous, base load, load following, and peak shaving applications. However, for standby and emergency applications where the utility grid is not available, an external energy source (such as batteries, for example) is required for starting. In addition, since the turbogenerator can utilize a recuperator for improving overall cycle efficiency and the recuperator stores a significant amount of thermal energy, an external energy sink may be required to dissipate this energy when offloading the turbogenerator during standalone operation.
Unlike reciprocating engine generator sets that possess significant inertial mass for dissipating energy, the turbogenerator's low inertial mass of the rotating components (shaft, compressor, turbine, and permanent magnet rotor) requires an external heat sink for offloads. The low inertial mass properties of the turbogenerator also increase the energy storage requirements of the external energy source as a result of inrush currents for turbogenerator starts.